Hi everybody. Since quite a few gurus frequent this board, I decided to ask a question that has been nagging me: How does the kernel calculate the processor speed? I am running SuSE 9.2 Professional on a Compaq Presario 3000Z laptop (2.2 GHz AMD64, 512 MB RAM, 60 GB HD, nVidia 440 toGo). For the record, I am also running 32-bit SuSE 9.2 Professional on a 32-bit Sony Vaio PCG-K35 so, I got two great distributions for the price of one and a great manual (so much for the British 'Linux Format' Magazine, which claims that SuSE is great but expensive!). The reason I ask this question is the following: My Presario laptop had a series of hardware problems, one of them being overheating. I had to send it to HP for repairs three times. After I got it back the third time, everything seemed to run fine except that the evaluation version of the burnin software I downloaded from www.passmark.com reports 1795 MHz (under Windows XP Home; the "speedometer" in the system tray of Windows has also disappeared). Under Linux, the KDE power manager and 'powersave -r' do show 2200 MHz occasionally. Does the kernel use the real time clock to come up with these values? The CPU does show up as a 2.2 GHz one. Does the kernel assume the maximum processor speed is what the processor reports at powerup (2.2 GHz in this case) and calculate the speed of the CPU based on that number (accounting for throttling)? If so, could a 2.2 GHz processor be actually run at 1.8 GHz and the kernel still report 2.2 GHz? I would appreciate your responses. CF
Constantine 'Gus' Fantanas
Hi everybody.
Since quite a few gurus frequent this board, I decided to ask a question that has been nagging me: How does the kernel calculate the processor speed? I am running SuSE 9.2 Professional on a Compaq Presario 3000Z laptop (2.2 GHz AMD64, 512 MB RAM, 60 GB HD, nVidia 440 toGo). For the record, I am also running 32-bit SuSE 9.2 Professional on a 32-bit Sony Vaio PCG-K35 so, I got two great distributions for the price of one and a great manual (so much for the British 'Linux Format' Magazine, which claims that SuSE is great but expensive!).
The reason I ask this question is the following: My Presario laptop had a series of hardware problems, one of them being overheating. I had to send it to HP for repairs three times. After I got it back the third time, everything seemed to run fine except that the evaluation version of the burnin software I downloaded from www.passmark.com reports 1795 MHz (under Windows XP Home; the "speedometer" in the system tray of Windows has also disappeared). Under Linux, the KDE power manager and 'powersave -r' do show 2200 MHz occasionally. Does the kernel use the real time clock to come up with these values? The CPU does show up as a 2.2 GHz one. Does the kernel assume the maximum processor speed is what the processor reports at powerup (2.2 GHz in this case) and calculate the speed of the CPU based on that number (accounting for throttling)? If so, could a 2.2 GHz processor be actually run at 1.8 GHz and the kernel still report 2.2 GHz?
The system scales the cpufrequency depending on your load - this is controlled with the powersave command. My cpu uses 2 Ghz normally but scales down to 800 Mhz or 1.8 Ghz with low load. Check the supported frequencies on your system like: $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies 800000 1800000 2000000 Andreas -- Andreas Jaeger, aj@suse.de, http://www.suse.de/~aj SUSE Linux Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GPG fingerprint = 93A3 365E CE47 B889 DF7F FED1 389A 563C C272 A126
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Constantine 'Gus' Fantanas told me that:
How does the kernel calculate the processor speed?
See a short program compute_MHZ.c at http://www.logix.cz/michal/devel/various/ Basically it reads the TSC register which counts processor clock cycles in two distinct times and divides by microseconds passed. Michal Ludvig - -- * A mouse is a device used to point at the xterm you want to type in. * Personal homepage - http://www.logix.cz/michal -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.5 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFB48UZDDolCcRbIhgRAtASAJ9hqovpr8yfxjoSThQNCHUcc7GLiwCbBBgp CQdwRbG46Mvg6Dcm4UzB2lA= =McgK -----END PGP SIGNATURE-----
participants (3)
-
Andreas Jaeger -
Constantine 'Gus' Fantanas -
Michal Ludvig